1. Field of the Invention
The present invention relates to a display device having an image capture function.
2. Related Art
A liquid display device has an array substrate provided with signal lines, scanning lines and pixel thin film transistors (TFTs), and drive circuits that drive the signal lines and the scanning lines. Along with recent advancement and development of integrated circuit technology, a process technique of forming a part of the drive circuit on the array substrate is put into practical use. Based on this technique, a liquid display device can be made thin and compact in total, and is widely used as a display device for various kinds of portable instruments such as portable telephones and laptop personal computers.
A display device having image capture function is proposed, in which closely arrayed area sensors (i.e., a photoelectric transfer element) are disposed on the array substrate (see for example, Japanese Patent Application Laid-open Nos. 2001-292276 and 2001-339640).
A conventional display device having this kind of image capture function changes a charge of a capacitor connected to a photoelectric transfer element according to the amount of light received by the photoelectric transfer element, and detects voltages at both ends of the capacitor, thereby capturing an image.
Recently, a technique of forming an image TFT and a drive circuit onto the same glass substrate according to a polycrystalline silicon (i.e., polysilicon) process is developed. The photoelectric transfer element can be also formed onto each pixel easily according to the polysilicon process.
When a display element and a photoelectric transfer element are incorporated into the pixel of the display device, the number of control lines to control the display elements and the photoelectric transfer elements increases, thereby lowering an aperture ratio. When the number of control lines increases, the area of the control circuit connected to the control lines also increases, resulting in an increase in the frame area of the array substrate.